1. Field of the Invention
This invention relates to a laser spraying process.
2. Prior Art Statement
A laser spraying process is one in which a spraying material is supplied to and melted in a high energy density zone formed by converging a laser beam therein with a converging lens or a mirror so that the molten material is driven as particles by a carrier gas stream to a target surface to form a film of the spraying material on the surface.
Spraying processes prior to the development of the laser spraying process include a flame spraying process, a plasma spraying process and a wire explosion spraying process. With the development of the laser spraying process, it has become possible to readily form a high energy density zone to obtain a spraying material film having reliable adhesion.
Well-known laser spraying processes are disclosed in Japanese Patent Publication No. 61-45494, Japanese Patent Disclosure No. 61-163258, Japanese Patent Disclosure No. 61-264168 and Japanese Patent Disclosure No. 62-177166.
In the laser spraying process disclosed in Japanese Patent Publication No. 61-45494, a laser beam is converged by a parabolic mirror onto a base surface, and a spraying material in the form of particles is fed by a heated shield gas stream to the base surface, on which the laser beam is converged, to heat the base and spraying material so as to melt and deposit the spraying material on the base surface.
In the laser spraying process disclosed in Japanese Patent Disclosure No. 61-163258, a laser beam is converged by an optical lens onto a base surface, while a powdery spraying material is fed to and heated in the laser beam to blow the material against an area of the base surface on which the laser beam is incident, thus forming a spraying material film on the base surface.
The laser spraying processes disclosed in Japanese Patent Disclosures No. 61-264168 and 62-177166 were proposed by the inventors. These processes have the aim of increasing the adhesion between a base surface and a spraying material film formed thereon by heating the base surface with a laser beam after formation of a high energy density zone.
The above four earlier inventions are based on the concept that by feeding a molten spraying material to a preliminarily heated base surface, the adhesion between a base surface and a spraying material film formed thereon can be increased so as to reduce the separability of the spraying material film. This has been inferred from the result of past research showing that the quality of a junction formed in welding, soldering or deposition can be enhanced by preheating the base surface.
However, in order to heat the base surface with the laser beam after formation of the high energy density zone as noted above, it is necessary to provide, in addition to a carrier gas feeder, a device for leading the laser beam to the base surface, thus complicating the overall apparatus. In addition, the base surface is sometimes heated to the neighborhood of 1,400.degree. C., and feeding the spraying material to such a heated base surface is liable to cause reaction of the material constituting the base surface and molten particles of the spraying material so as to produce undesired alloys. Further, since the base surface is heated to a high temperature, the base should not consist of a material which can be readily thermally broken or deformed.